Some data storage media may be used in both computers and in consumer devices such as video or audio players. However, for some media types, formats for consumer applications and formats for computer applications may be incompatible. For example, the term DVD (also referred to as digital versatile disc, or digital video disk) describes a physical medium having a standard size, but there are many proposed logical formats for use in recording video data, audio data, and computer data, some of which are incompatible. One particular requirement leading to format incompatibility is the requirement for defect management.
Recording of digital data, particularly on rewriteable media, is rarely defect free. Typically, data storage is broken into addressable units, and each addressable unit may include overhead data for error detection. It is also common to combine addressable units into larger blocks for error correction. Finally, for computer data, where data integrity is essential, it is common to reserve areas of a data storage medium for replacements, wherein if an addressable unit or block is unusable, a replacement addressable unit or block may be used instead. During reading of computer data, if a drive detects a unit or block that has been marked as defective, the drive determines where the replacement is stored (the logical address is mapped to a different physical address), and reads the replacement. Typically, some delay time (called latency) is required to access the replacement. Another form of defect management can exist within a host computer, specifically within a file system. However, video and audio players typically do not interact with a host computer file system, and this type of defect management is not relevant to the present application.
Replacement blocks are typically not used for digital video or digital audio data. First, digital video and digital audio is often recorded on stamped media, where defects are inherently fewer than for write-once or rewriteable media. Second, digital video or digital audio is relatively tolerant of data errors so that there is typically no need for replacements. For example, a single uncorrected error in video data might cause a visual defect or loss of synchronization that lasts at most for a few milliseconds. The human perception system (sight, sound, and touch) tends to integrate, filter, and interpolate discontinuities so that many defects are not perceived, or are acceptable. In addition, many video and audio players may filter or otherwise compensate for discontinuities. Third, video and audio applications require a continuous stream of data, and the latency required to skip a defective data unit and to read a replacement data unit may be unacceptable. In particular, if replacement areas are interleaved with the data areas, a replacement area then causes a relatively long discontinuity in the video or audio data stream as the drive seeks around each replacement area.
It would be useful if a drive could write a DVD medium using one format that could be used universally for digital computer data, digital video data, and digital audio data. Defect management, in particular replacement, is required for DVD computer data, and replacement is incompatible with present DVD video players. There are proposals for defect management that require a new video drive design that can accommodate replacement. There is a need for DVD defect management that is compatible with present DVD video players.